1. Field of the Invention
The present invention relates to an apparatus for detecting the line of sight of the eye and an optical apparatus having the same, and more particularly to an apparatus for detecting the line of sight of the eye and an optical apparatus having the same that detects the axis of a looking direction of an observer, that is, the so called line of sight of the eye (the visual line), by making use of an image reflected from the eyeball obtained by illuminating the surface of the eyeball of the observer with light to perform a variety of photographing operations.
2. Related Background Art
Hitherto, a variety of apparatuses (for example, an eye camera) for detecting the position on the observed surface observed by an observer, that is, detecting the line of sight of the eye (the visual line) have been disclosed.
For example, Japanese Patent Application Laid-Open No. 1-274736 discloses a technology arranged in such a manner that parallel light beams emitted from a light source are used to irradiate the front portion of the eyeball of an observer, and a cornea reflection image formed by light reflected by the cornea and the imaging position of the pupil are utilized to obtain the visual line.
The position in the visual field of the finder which is observed by an observer can be obtained by detecting the rotational angle of the eyeball of the observer. The accuracy of detecting the rotational angle depends upon the image forming magnification of an optical system for detecting the line of sight of the eye.
If the image forming magnification of the optical system for detecting the line of sight of the eye is reduced, the quantity of movement of the eyeball image formed on the surface of an area-type sensor with respect to the rotation of the eyeball is made smaller. Therefore, the quantity of the change between the image of the light source reflected by the cornea and the center of the pupil becomes small. In this case, the accuracy in detecting the line of sight of the eye deteriorates.
Although the accuracy in detecting the line of sight of the eye can be improved by enlarging the image forming magnification of the optical system for detecting the line of sight of the eye, the area of the light receiving portion of the area-type sensor is enlarged excessively. In this case, a problem arises in manufacturing the apparatus and another problem of excessively large cost takes place.
If the pitch of pixels of the sensor is lengthened, the quantity of movement of the image of the eyeball formed on the surface of the sensor with respect to the rotation of the eyeball is made smaller. In this case, the accuracy in detecting the line of sight of the eye deteriorates.
Although the accuracy in detecting the line of sight of the eye can be improved by shortening the pitch of the pixels of the sensor, the number of pixels to be subjected to a calculation process is increased. Therefore, time taken to complete the detection of the line of sight of the eye becomes longer and a problem in practical use arises. Further, the cost of the sensor cannot be reduced and the S/N ratio can easily be lowered because the light receiving area for one pixel is reduced.
Since the finder system of a camera has a wide horizontal directional visual field and the line of sight of the eye of an observer can easily be moved horizontally if the camera is held at a conventional attitude, the apparatus for detecting the line of sight of the eye must have an improved accuracy in detecting the line of sight of the eye in the horizontal direction. However, conventional apparatuses for detecting the line of sight of the eye have not been designed from the foregoing viewpoint.